This invention relates to method and apparatus for detecting and integrating chromatographic peaks.
In a typical chromatographic analysis the widths of the peaks normally vary by a factor of at least ten and usually by a factor of forty or so. Depending upon the particular analysis being run, there may be some pattern to the variation in the peak widths or there may be no pattern.
In using automated equipment for integrating the area under the peaks (to provide automated analysis of the samples being run), it is important to match the time constant of the filter detector used for integrating a peak with the width of the peak.
If the time constant of the filter detector is too short, the integrating equipment becomes insensitive to broad peaks. Broad peaks may be missed altogether, or all of the area under the peak may not be completely recovered.
If the time constant of the filter detector is too large, the automated equipment may miss peaks that are too narrow to be detected. The narrow peaks may look like noise. The automated equipment, in this case, might also tend to fuse adjacent narrow peaks together and integrate the fused peaks as one peak, rather than separately.
The prior art has varied the time constant of a filter detector as the chromatographic analysis is being run to try to match the filter detector to the signal being monitored.
In one prior art technique the assumption was made that the peaks will double in width ever so often. The time constant of the filter detector was adapted at specific times in a chromatogram to accommodate the predicted changes in the peak widths. This technique worked fairly well but had limitations, particularly with temperature or solvent programmed chromatograms.
A more recent technique measured the characteristics of a peak being integrated and then used that knowledge to predict the characteristics of a peak to be subsequently integrated. This technique also has undesirable limitations, particularly if there is too long a time interval between adjacent peaks.